Electromagnetic pressure gauge



Jan. 25, 1949. 2,460,076

J. F. EMERSON ELECTROMAGNETIC PRESSURE GAUGE Filed Feb. 24, 1947 23 Zzz,

' INVENTOR Ja/m E1-C/776/150/7 ill]; 7

ATTORNEY In-a Patented Jan. 25, 1949 UNITED STATES PATENT OFFICEELECTROMAGNETIC PRESSURE GAUGE John F. Emerson, Hasbrouck Heights, N.J., as-

signor to Kearlott Company, Inc., New York, N. Y., a corporation of NewYork Application February 24, 1947, Serial No. 730,484

4 Claims. 1

of the above type in which the direction of maxi mum stress of themagnetic material coincides with the direction Of the flux path.

Another object is to provide a novel and improved device of the abovetype which is insensitive to mechanical vibration.

Other objects and advantages will be apparent as the nature of theinvention is more fully disclosed.

In accordance with the present invention a transformer is formed with aclosed core which includes as one element a hollow cylindrical casing orcontainer to which fluid pressure may be applied. The container is soarranged that the fluid pressure stresses the Walls thereof in thedirection of flux flow and thereby varies the reluctance of the magneticcircuit. For increasing the sensitivity of the device the containers aremade of a magnetic material th permeability of which changes in oppositesense when subjected to compression than when subjected to tension and apair of containers are arranged to be differentially stressed by theapplied pressure so that one container is placed under compression andthe other under tension. The efiects are thus made additive.

In one embodiment the containers are disposed in a closed chamber whichis arranged so that different fluid pressures may be applied to theinside and outside of the containers. The walls of the containers arethus stressed by the pressure to be measured and the resultant changesin permeability may be utilized as an indication of this pressure.

Although the novel features which are believed to be characteristic ofthis invention are pointed out more particularly in the claims, thenature of the invention will be better understood by reierring to thefollowing description, taken in connection with the accompanying drawingin which a specific embodiment thereof has been set forth for purposesof illustration.

In the drawings:

Fig. 1 is a longitudinal section through a pressure sensitive deviceembodying the present in- 2 vention, with the electric circuitsindicated schematically; and

Fig. 2 is a transverse section through the device taken on the line 2-2of Fig. 1.

Referring to the drawings more in detail, the device is shown ascomprising a closed vessel II having a cylindrical wall II and end wallsl2 and H. A central transverse partition I4 divides the vessel Ill intotwo compartments iii and I6. Pipes l1 and I8 extend through the endwalls l2 and i3 respectively to suppl fluids, the differential pressureof which is to be measured, to the respective compartments l5 and I6. Ifthe pressure difference between two fluids is to be measured therespective fluids are applied to the pipes l1 and I8. If, however, thepressure of a single fluid only is to be measured, such fluid may besupplied to one of the pipes H or I! and the other of the pipes mayremain open to the atmosphere or may be sealed to maintain a constantpressure in the corresponding compartment. Transformers 2| and 2| aremounted in the respective compartments l5 and IS. The transformer 20comprises a closed magnetic core 22, having a leg 23 carrying a primarywinding 24 and a secondary winding 25. The core 22 is shown as supportedby struts 26 attached to the side wall II. A closed cylinder 30 isinserted in the return leg 24 of the core 22. This cylinder 30 includesa cylindrical side wall 3! and the walls 32 and 33 which are bowedoutwardly so as to be under compression in response to outside pressuresand under tension in response to inside pressures. The return leg 34 isattached to the side wall 3! at diametrically opposite points so thatthe magnetic path extends circumferentially around the cylinder. A pipe35 connects the interior of the cylinder 30 to a port 36 in thepartition 14, so that the interior of the cylinder 30 is maintained atthe pressure of the compartment IS.

The primary winding 24 is connected by leads 28 and 40 to terminal posts4| and 42 which extend through the cylindrical wall II and are insulatedtherefrom by suitable means, shown as bushings 43 and 44. The secondarywinding 25 is connected by leads 49 and 50 to terminal posts 5| and 52which also extend through the Wall H and are insulated therefrom bymeans shown as bushings 53 and 54.

The transformer 2! comprises a magnetic core 60 having a leg 0| carryinga primary winding 62 and a secondary winding 63. The core 5! is shown assupported by struts 64 attached to the side wall II. The return leg 10of the core in- 66 cludes a closed cylinder having a cylindrical 3 sidewall 88 and end walls 87 and 88 which are bowed outwardly similarly tothe end walls 32 and 33 of the cylinder 30. The return leg I 01' thecore 80 is attached to the side wall 88 at diametrically opposite pointsso that the magnetic path extends circumferentially around the cylinder.A pipe II connects the interior of the cylinder 85 to a port 12 in thepartition I4, so that the interior of the cylinder 85 is maintained atthe pressure of the compartment I5.

The primary 82 is connected by leads I5 and 18 to terminal posts 11 and18 which extend through the cylindrical wall II and are insulatedtherefrom by bushings I8 and 80 respectively. The secondary 83 isconnected by leads 8| and 82 to terminal posts 83 and 84 which extendthrough the cylindrical side wall II and are insulated therefrom bybushings 85 and 88 respectively.

The primaries 24 and 82 are connected in series to a suitable source ofalternating current 80 by leads 8|, 82 and 83 which are connected to theterminal posts H, 42, I1 and 13.

The secondary windings 25 and 83 are series connected to a potentiometer85 by leads 08, 81 and 88 which are connected to terminal posts II, 52,83 and 84. A voltage indicating instrument such as a voltmeter I00 isconnected in a bridge circuit by leads IN and I02 between the lead 81which connects the terminal posts 52 and 88 and a variable tap I03 onthe potentiometer 85.

In the operation of this device, a fluid whose pressure is to bemeasured is supplied through the pipe I8 to the compartment I8 andthrough the pipe to the interior of the cylinder 30. The pipe I! remainsopen to the atmosphere or the compartment I5 may be sealed at a flxedpressure which is also supplied through the pipe II to the interior ofthe cylinder 85. If the diilerence between two fluid .pressures is to bemeasured, one fluid is supplied by the pipe I8 to the compartment I8 andthe other fluid is supplied by the pipe I! to the compartment I5.

With the compartments I5 and subjected to the same pressures, forexample atmospheric, the transformers 20 and 2| are designed to haveequal permeabilities so that equal voltages are induced in thesecondaries 25 and 83 and, if the bridge circuit is properly balanced, azero indication is obtained on the voltmeter I00. The tap I08 may besuitably adjusted to effect such balanced condition when bothcompartments are at atmospheric pressure.

When the pressures to be measured are supplied to the compartments I5and I8 so as to establish a pressure differential therebetween, one ofthe cylinders 80, 85 will be subjected to external pressure which placesthe walls thereof under compression and the other cylinder will besubjected to internal pressure which places its walls under tension.Thewalls of the cy- 80 and 85 are formed of a material such linders as'a molybdenum-nickel-iron alloy which has the property of increasing itspermeability under tension and ,decreasing its permeability undercompression, or vice versa. Hence the permeability of the walls of oneof the cylinders 30, 85 is increased and that or the other cylinder isdecreased, with the result that the voltage produced by one of thesecondaries 25, 83 is increased and other decreased. The balance of thebridge circuit is accordingly upset and a voltage is produced across thevoltmeter I00 which is a function of the pressure diiference between theapplied fluids. The voltmeter I00 may of course be graduated to readdirectly in pressure units instead of in voltage and may constitute adirect reading pressure indicating device.

It will be noted that the side walls 3i and 88 of the cylinders and arestressed circumferentially by either the compressive or expansive forcesto which they are subjected. Likewise, the flux in the return paths ofthe respective transformers flows circumferentially around the walls 8Iand 88. Hence the direction oi stress coincides with the direction ofthe flux flow and the maximum change in flux is produced by thevariations in the stress to which the respective walls are subjected.

It is to be understood that the meter I00 may be replaced by a follow-updevice which is adapted to drive the variable tap I08 to a position suchthat a zero voltage is obtained across the instrument I00, or the tapI08 may be ad-,

justed manually so as to obtain a zero voltage. In either case thepressure diiferential will be measured by the displacement of the tapI08, and a suitable scale may be incorporated with the potentiometer forthis purpose.

The secondaries 25 and 83 may of course be connected in opposition tothe voltmeter I00 so as to indicate directly the unbalance in voltagesin the two secondaries, or the windings may be connected in seriesopposition and the voltage from the follow-up potentiometer connected tocancel the diflerential voltage.

Inasmuch as the two transformers 20 and 2| are mounted in a parallelposition in the side wall II of the casing I0 they will be equallyaffected by mechanical disturbances, such as the vibration of thesupport on which the device may be mounted, and the effect thereof onthe respective cores will be balanced out. Hence the device iscomparatively insensitive to mechanical vibrations and constitutes anaccurate pressure gauge for measuring fluid pressures.

The device may also be usedto measure mechanical pressures which may beapplied to stress the respective cylinders, although it is particularlyadapted to the measurement of fluid pressures and has been so described.

Although a specific application of the invention has been shown forpurposes of illustration, it is to be understood that the invention maybe applied to various uses and that changes and adaptations may be madetherein as will be readily apparent to a person skilled in the art. Theinvention is only to be limited in accordance with the scope of thefollowing claims.

What is claimed is:

1. An electromagntic pressure gauge for measuring fluid pressures,comprising a closed container having a cylindrical wall of a magneticmaterial the permeability of which varies as a function of themechanical stress to which it is subjected, magnetic members attached tosaid wall at diametrically opposite points and with said walls forming aclosed core in which the flux passes circumferentially around saidwalls, primary and secondary windings, carried by said magnetic members,means supplying the fluid pressure to be measured to said container tostress the walls thereof and thereby vary the reluctance of said core, acurrent source connected to energize said primary winding and a voltageresponsive device connected to said secondary winding.

2. An electromagnetic pressure gauge for measuring fluid pressures,comprising a closed casing 75 having an internal partition dividing saidcasing nto a pair of pressure compartments, means in- ;roducing fluidpressures to be measured into the :espective compartments, a variableimpedance ievice mounted in each compartment, each of said devicescomprising a closed container having a cylindrical wall of a magneticmaterial the permeability of which varies as a function of themechanical stress to which it is subjected, magnetle members attached tosaid wall at diametrically opposite points and with said walls forming aclosed core and a winding carried by said magnetic members, meansconnecting the interior of each container to receive fluid pressure fromthe opposite compartment whereby the walls of each container arestressed by the differential efiect of said fluid pressures, and meanscomparing the impedances of said devices.

3. An electromagnetic pressure gauge for measuring fluid pressures,comprising a closed casing having an internal partition dividing saidcasing into a pair of pressure compartments, means introducing fluidpressures to be measured into the respective compartments, a variableimpedance device mounted in each compartment, each of said devicescomprising a closed container having a cylindrical wall of a magneticmaterial the permeability of which varies as a function of themechanical stress to which it is subjected, magnetic members attached tosaid wall at diametrically opposite points and with said walls forming aclosed core and a winding carried by said magnetic members, meansconnecting the interior of each container to receive the fluid pressurefrom the opposite compartment whereby the walls of each container arestressed by the differential effect of said fluid pressures, a bridgecircuit connected to said windings, and a voltage responsive deviceconnected in said bridge circuit to show zero voltage when theimpedances of said windings are equal and to show a voltage which is a40 function of the unbalance produced by differential pressures in saidcompartments.

4. An electromagnetic pressure gauge for measuring fluid pressures,comprising a closed casing having an internal partition dividing saideasing into a pair of pressure compartments, means introducing fluidpressures to be measured into the respective compartments, a transformermounted in each compartment, each of said transformers comprising aclosed container having a cylindrical wall of a magnetic material thepermeability of which varies as a function of the mechanical stress towhich it is subjected, mag-- netic members attached to said wall atdiametrically opposite points and with said walls forming a closed coreand primary and secondary windings carried by said magnetic members,means connecting the interior of each container to receive fluidpressure from the opposite compartment whereby the walls of eachcontainer are stressed by the differential effect of said fluidpressures, a current source connected to energize said primaries, abridge circuit connected to said secondaries, and a voltage responsivedevice connected in said bridge circuit to indicate the unbalancebetween the secondary voltages due the differential pressures.

JOHN F. EMERSQN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1 2,269,760 Eldredge Jan. 13,1942 2,376,156 Kuehni May 15, 1945 FOREIGN PATENTS Number Country Date311,436 Germany Apr. 25, 1918 832,891 France Oct. 4, 1938

